The present invention is directed to the field of electrical contacts for switch mechanisms.
Switch mechanisms which may, for example, be employed in a calculator type keyboard typically consist of a conductive spring material spaced from conductors mounted on a dielectric substrate such as a printed circuit board. When the spring member is urged against the conductors, contact closure is made and the switch is closed. Some switch mechanisms include provisions by which contact elements are wiped against each other as closure takes place so as to produce a contact cleaning action to maintain electrical characteristics of the switch mechanism over a relatively large number of operations. However, where a switch mechanism includes contact elements which cannot be caused to wipe against each other, other provisions for maintaining the electrical characteristics of the switch mechanism should desirably be provided.
Where the contact elements comprise flat surfaces which contact each other without a wiping action, it may be necessary to coat their surfaces with a precious metal such as gold or silver. This is costly. Furthermore, even with such a coating, should foreign matter become lodged between the surfaces of the two contact elements, no contact closure will occur because there is no wiping action available to dislodge the foreign matter.
So that foreign matter cannot readily be lodged between two contact surfaces, one of the contact surfaces may be provided with a raised portion. A switch mechanism including a contact with a raised portion is described, for example in U.S. Pat. No. 3,886,341. However, because of the manner in which these raised portions are formed, e.g., by bending or otherwise deforming a separate piece of metal, they cannot be readily employed with contacts which comprise conductors of a printed circuit board.